Electrostatic writing and printing device



2 Sheets-Sheet 1 c. K. CLAUER ETAL Oct. 29, 1963 ELECTROSTATIC WRITINGAND PRINTING DEVICE Filed Oct. 27, 1960 INVENTORS. CALVIN K. CLAUER'JACK D. KUEHLER ATTORNEY Oct. 29, 1963 c, K. CLAUER ETAL 3,109,062ELECTROSTATIC WRITING AND PRINTING DEVICE Filed Oct. 27, 1960 2Sheets-Sheet 2 United States Patent ()flice 3,109,062 Patented Get. 29,1963 3,109,062 ELECTRQSTATIC WRITING AND PRINTKNG DEVICE Calvin K.Clauer and Jack D. Kuehler, San Jose, Calitl,

assignors to international Business Machines Corporation, New York,N.Y., a corporation of New York Filed @ct. 2.7, 1960, Ser. No. 653%Claims. (Cl. 1'78--7.5)

The present invention relates in general to electronic display devicesand relates more particularly to apparatus for producing a visibledisplay of information represented by an information-bearing electricalsignal which is converted to an electrostatic charge distributionpattern.

There are numerous applications where it is desirable to provide astatic visual display of information transmitted in the form ofelectrical signals, such as those transmitted over a video communicationlink. The conventional method of displaying such information is, ofcourse, through a cathode ray tube having a phosphor coated face onwhich an electron beam impinges to produce a visible display in responseto the information which modulates either the intensity or thedeflection of the electron beam. However, the use of phosphors fordisplays of the type contemplated herein is not particularlysatisfactory, owing to the persistence problems associated with mostphosphors, which necessitates frequent scanning of the phosphor tomaintain the stationary image visible. This requirement of frequentscanning is objectionable both from the standpoint of the bandwidthrequirements which it places on the transmitting link and also from thestandpoint of registration problems on successive scans, since it isdifficult to produce exact registration on successive scans of anelectron beam over a phosphor tube face.

An alternative prior art solution which is somewhat more satisfactoryfor the purposes of producing a visible display involves the formationof an electrostatic image of the information to be displayed on a targetsurface in an evacuated envelope, and the dusting of this electrostaticimage with small particles of an opaque material. These particles aredeposited on and attracted to the electrostatically charged surface toproduce a visual indication of the information represented by theelectrostatic charge distribution. In this prior art embodiment,however, the charged particles which are attracted to theelectrostatically charged member to form the visible image are disposedclosely adjacent the target surface during the writing on or charging ofthe electrostatic target surface, and it is necessary to keep theelectrostatic target surface continuously vibrated during writing toprevent the charged particles from adhering to the target surface duringthe writing. In one embodiment of this prior art structure, the chargedparticles are disposed between the electron writing beam and the targetsurface and are maintained in a cloud adjacent the target surface as aresult of the vibration of this surface during writing. However, thedisposition of the charged particles between the target surface and theelectron beam is objectionable in that the interaction between thewriting beam and the particles makes it difficult to obtain the desiredresolution of the beam on the electrostatic target surface. In anotherembodiment of this prior art device, the charged particles are disposedon the opposite side of. the target surface from the writing beam andhence do not interfere with the Writing beam, but the particles in thisembodiment still are disposed closely adjacent or on the target surfaceand are kept from the target surface only by the continual vibration ofthe target surface during writing. This embodiment, While eliminatingthe possibility of interference between the Writing beam and thevibrating particles, still is objectionable in that the particles areclosely adjacent the vibrating target surface during writing and hencemay be infiuenced by the electrostatic field during the writing. It willbe appreciated that both of these prior art embodiment also present asubstantial problem in maintaining the writing electron beam in thedesired areas of the vibrating target surface.

The present invention contemplates apparatus in which an electrostaticimage is formed by an electron beam directed toward an electricallynon-conductive surface capable of storing electrostatic charges in smalldiscrete areas thereof. The electrostatic target surface is disposed inone end of an evacuated envelope having a transparent window or faceplate therein. The target surface is disposed adjacent to but spacedfrom the transparent window, and disposed in the space between thetarget surface and the transparent window is a supply of small particlescapable of retaining an electric charge and of a suitable color toproduce a visible image.

During writing of the electrostatic charge pattern on the front surfaceof the target surface, these particles are maintained out of theinfluence of the electrostatic field. Upon completion of theelectrostatic writing on the target surface, the charged particles arecascaded across the rear or reverse side of the target in some suitablemanner. The electrostatic field resulting from the deposition ofelectrical charges in different discrete areas of the target surfaceextends through the thin target member and exerts an attractive force onthe cascading charged particles, causing them to adhere to the reverseside of the target surface in the charged areas thereof. The adherenceof the suitably colored charged particles to the oppositely chargedareas of the target surface produces a visible image of the informationwhich had been written on the target surface in the form of anelectrostatic charge distribution pattern. The visible image may then beViewed or photographed through the transparent face plate at the end ofthe evacuated envelope or utilized in any other manner, depending uponthe nature of the application.

When it is desired to erase the electrostatic image and the visibleimage, a flood beam of electrons within the envelope is activated toflood the charged side of the target surface with electrons. Theaccelerating velocity of the electron beam forming the flood beam issuch in relation to the secondary emission properties of the insulatingmaterial forming the target surface that the secondary emission ratiofrom the target surface is greater than unity under the action of theelectron flood beam. This means that for every incoming electron fromthe flood beam, more than one electron leaves thetarget surface, untilequilibrium is reached and the electrostatic charge on the targetsurface has been removed. The flood beam is then turned off and thetarget surface is available for storage of the next electrostatic imagethereon.

Objects and advantages of the present invention in addition to thosediscussed above will be apparent from the following description whenread in connection with the accompanying drawings, in which:

FIG. 1 is a perspective view, partly in section, illustrating the oneembodiment of the present invention for forming an electrostatic imageon a target surface Within an evacuated envelope and for producing avisible image from this electrostatic image;

FIG. 2 is a perspective view illustrating one method of cascading thecharged particles across the charged electrostatic target surface byrotation of the evacuated envelope forming the tube of the presentdevice; and

FIG. 3 is a perspective view illustrating an alternative embodiment ofthe present invention in which the target surface is movable within theevacuated envelope, such movement of the target surface being producedafter com- U, pletion of the charging of the electrostatic targetsurface to cascade the charged particles across the back of the targetsurface.

Referring to FIG. 1 by character of reference, numeral 11 designates anevacuated envelope of a suitable material, such as glass or metal inwhich the electrostatic storage apparatus operates. Envelope 11 may beof any suitable shape, such as that of a conventional cathode ray tubehaving means at one end thereof for generating a beam of electrons andhaving at the other end thereof an enlarged face plate member. As shownin the drawing, the electron beam generating means includes a cathode11c and a grid 11g to which modulating signals me applied to regulatethe intensity of the electron beam emitted from the electron gunelements including cathode 110. The modulating input signalsrepresenting information to be stored and visibly displayed on thedevice of the present inveniton may be from any suitable source, such asfrom a video output device represented schematically at 12. Video inputnetwork 12 applies a modulating input to grid 11g relative to thecathode structure to modulate the electron emission in response tovariations in the input information signals. The modulated electron beamis preferably swept across the target surface by suitable deflectionmeans, such as a deflection yoke 11d disposed around the neck ofenvelope 11. Deflection yoke lid is energized by a suitable source ofsweep voltage signals, such as the sweep voltage generator 13. Asindicated,

sweep voltage generator 13 may receive a synchronizing pulse from thevideo signal source 12 through a conductor 14 to synchronize thebeginning of the beam sweep with the start of the information signals tobe displayed.

Envelope 11 is provided at the end opposite the electron beam generatingmeans with a transparent face plate member He. Transparent face platewindow 116 may be a unitary part of envelope 11 or may, as shown, be aseparate element which is secured to the end of envelope 11 in air tightrelation by suitable means such as screws 11f. Face plate 11a isprovided with an electrically conductive transparent coating on itsinner surface to provide for connection of a source of acceleratingvoltage, as will be described more in detail below.

Spaced from but adjacent to the transparent window member 1112 is anelectrical insulating member 16 on which the electrostatic charge isplaced by the controlled beam and to which the charged particles adhereto produce a visible image of the electrostatic charge distributionpattern. Insulating material 16 may be of any suitable type such as thepolyester resin film marketed under the trade name Mylar by E. I. duPont de Nemours. Another suitable material is a polyvinyl fluorideimpregnated with titanium dioxide to produce a white opaque sheetmember, the material beingmarketed under the trade name Teslar by E. I.du Pont de Nemours.

Insulating member 16 is preferably very thin and we have found forexample that a sheet of Teslar or a sheet 'of type C Mylar of /2 milthickness is very suitable. Member 16 is mounted in the evacuatedenvelope .by suitable means, such as a clamping ring 17 having'separablehalves between which the member 16 is tightly stretched. Clamping ring17 may then be firmly seated against a shoulder in the end of envelope11 to hold target member 16 firmly in positionin the enlarged end ofenvelope 11.

In the space between member 16 and transparent window member 11a thereis provided a plurality of small particles of electrical insulatingmaterial which are capable of retaining an electrical charge. Suchparticles 21 are preferably of a dark color so as to produce a maximumcontrast with the insulating member 16 when the particles adhere theretoin response to the electrostatic charge distribution pattern. Particles21 may be charged in any suitable manner, such as through thetriboelectric effect in which the particles 21 to be charged are mixedwith other particles 23 of a dissimilar nature so that agitation of thetwo dissimilar particles produces opposite electrical charges thereon.The two types of particles utilized may be of any suitable type havingthe required relationship in the triboelectric series. One example ofsuitable materials is the use of resin or plastic particles 21 and smallglass beads as particles 23. The granular particles 21, beingelectrically insulated, retain their electrical charge after agitationwith beads 23 so as to be charged for attraction to the electrostatictarget surface 16. The charged particles 21 are disposed in the spacebetween electrostatic target member 16 and transparent window memberlie, but are maintained away from the target member 16 and theelectrostatic charge distribution pattern thereon during the writing onmember 16 by the modulated electron beam. In the embodiment illustratedin FIG. 1, it will be noted that charged particles repose in the bottomof envelope 11 behind clamping ring 17 and thus are maintained away fromthe charge existing on member 16. It will also be noted that the chargedparticles 21 are behind target member 16 and hence do not interfere withthe electron beam producing the electrostatic charge on member 16.

To remove the electrostatic charge distribution pattern and the chargedparticles adhering thereto from the target surface, means such as anelectron gun 22 may be utilized to generate a flood beam of electronsdirected at the writing side of target member 16. As shown in thedrawing, electron gun 22 extends through envelope l1 and is operativewhen energized to produce a large quantity of electrons which areaccelerated toward target surface 16. Flood gun 22 preferably operatesby producing a secondary emission ratio greater than unity for electronsstriking target surface 16. For many electrical insulating materials,such as the material of target member 16, the secondary emission ratiois greater than unity within a given range of accelerating voltagesapplied to electrons directed at the material. This means that withinthis range of accelerating voltages, for every incoming electron fromthe electron flood beam, more than one electron is emitted by secondaryemission from the target surface 16 until equilibrium is reached. Floodgun 22 is energized from an erase control network 24 which supplies asuitable potential between the cathode and grid of gun 22 to generate aflood beam so as to produce in material 16 a secondary emission ratiogreater than unity. This flood beam bombardment causes the electronsforming the electrostatic charge on member 16 to be removed from member16, thus dissipating the electrostatic charge on member 16 and preparingit for receiving another electrostatic charge pattern from the modulatedelectron beam. After erasure of the electrostatic charge pattern, theloose particles 21 are cascaded across the reverse side of target 16 toremove the charged particles adhering thereto.

Erase network 24 may be connected by a conductor 25 to the back half ofmetallic clamping ring 17 to apply a potential to this ring duringerasing. The application of this potential causes this half of clampingring 17 to act as .a collector electrode for the secondary emissionelectrons from target 16, thus preventing the return of these electronsto the target and thereby hastening the complete erasure ofelectrostatic charge distribution pattern on target 16.

In operation then, the information to be visibly displayed is suppliedin the form of video signals through video input network 12 to modulatethe intensity of the electron beam generated by the electron gunelements of tube 11. This modulated beam is deflected across the face oftarget surface 16 by means of the deflection signals supplied from sweepvoltage generator 13 to the deflection yoke 11d. As the modulatedelectron beam sweeps across target 16, it will produce thereon smalldiscrete areas of electrostatic charge in accordance with the beamintensity.

There is thus produced on target member 16 an electrostatic chargedistribution pattern varying in accordance with the informationrepresented by the video input signals supplied through network 12. Thiselectrostatic distribution pattern as written by the electron beam willbe invisible to the human eye, but will represent an electrostaticcharge distribution pattern corresponding to the information to bepresented.

Upon completion of the production of the electrostatic chargedistribution pattern on member 16, which pattern may be produced by asingle sweep of the electron beam across target member 16, a visibleimage of the pattern may be formed by cascading the charged tonerparticles 21 across the reverse side of target member 16 to causeparticles to adhere to the reverse side of target member 16 in thoseareas which have an electrical charge opposite to the charge of theparticles 21. In the illustrated embodiment it is assumed that thecharge produced on target 16 by the electron beam is a negative charge,and that the particles 21 receive a positive charge as a result of theiragitation with particles 23 in accordance with the triboelectric effect.However, it will be appreciated that these charge polarities could bereversed without aifecting the operation or" the invention. As thepositively charged particles 21 are cascaded across the reverse side ofmember 16, the negative charges on the different discrete areas oftarget 16 attract the charged particles to cause them to adhere to thetarget surface in those areas having a negative charge thereon. Since,as indicated above, the particles 21 are preferably of a dark color,they form on member 16 a visible image of the electrostatic chargedistribution which may be viewed or photographed through the transparentend window member 11c.

Cascading of the charged particles across the reverse side of thecharged target member '16 may be accomplished by any suitable means,such as manual manipul tion or rotation of envelope 11 to produce agravity flow of the charged particles across member 16 to produce thedesired adherence of the particles to the charged areas of the targetsurface. referably, however, the cascading is accomplished by automaticor semiautomatic means. FIG. 2 schematically illustrates one form ofapparatus for producing such cascading by rotating the envelope assemblyafter writing of the electrostatic charge distribution pattern. In FIG.2 the charged toner particles are disposed in a plurality of bucket-likedepressions 26 in the space bet-ween target member 16 and transparentwindow member He. Envelope 11 is adapted to be rotated by meansincluding a motor 27 which drives an idler wheel 28 engaging the rim ofthe enlarged end of envelope 11.

When motor 2'7 is energized, it drives Wheel 28 to rotate envelope 11through 180 of rotation, thus causing the charged particles 21 inbuckets to be carried around by the rotation until they are spilled fromtheir respective buckets and cascaded across the reverse Side of targetsurface 16, thus causing the charged particles to adhere to the chargedareas of member 16. Upon completion of this cascading, the direction ofrotation of motor 27 is reversed to rotate tube 11 in the reversedirection and return it to its initial position. By thus utilizing only180 of rotation, rather than a'compiete full circle of rotation,problems in connection with com-mutating the electrical connections tothe flood gun 22, deflection yoke 11d and the electron gun elements 110are eliminated, since the electrical leads to these elements may be madeof suitable length and flexibility to permit 180 rotation of envelope 11without disrupting the connections. By suitable design of the shape ofbuckets 26, they may be caused to retain particles 21 therein until eachbucket is almost at the top point in its rotation, thus producingmaximum coverage across the member 36 by the cascading particles.

FIG. 3 illustrates alternative apparatus for producing cascading of thecharged particles across the charged target member 16. In FIG. 3 thetarget member 16 is pivotally mounted within envelope 11 so that theassembly may be rotated within envelope 11 to produce the desired Circascading. As shown in FIG. 3, a transparent member 29 is secured to thereverse side of member 16 and spaced therefrom to form a chamber forholding charged particles 21 and particles 23. The assembly includingmember 16, charged particles 21 and cover plate 29 is rotatably mountedwithin envelope 11 on bearings 30 disposed within envelope 1-1. Inconnection with the embodiment of FIG. 3, it will be noted thattransparent end member 11s is spaced from the assembly includingelements 16, 21 and 29 a sufiicient distance to permit pivoting of theassembly on bearings 34 Within the tube.

The target assembly may be pivotally driven by any suitable means, butto reduce sealing problems in connection with the transmission ofpivotal movement through the walls of envelope 11 to the targetassembly, the drive is preferably in the form of a pair of magnetic members including an electromagnet 31 disposed outside envelope 11 adjacentbearing 30 and a soft iron member 32. Electromagnet 31, when energized,produces magnetic flux which extends through the wall of envelope 11 tolink with soft iron member 32 which is connected to the tar-getassembly, so that members 311, 32 form an electromagnetic clutch linkingthe target assembly within tube 11 to a drive shaft 33. Thus, withelectromagnet 31 energized, rotation of shaft 33 produces pivoting ofthe target as sembly including charged electrostatic target member 16,charged particles 21 and cover plate 29, to cause the particles tocascade across the reverse side of the target surface. After thiscascading, the direction of rotation of shaft 33 is reversed to returnthe target assembly to its initial position and to present the visibleimage thereon for viewing or other use through transparent end member11c. It will be noted that the use of electromagnetic coupling means 31,rather than permanent magnet means,

r eliminates any problems which might arise in connection with magneticinterference with the electron beam in sweeping across target surface16.

As an example of the operation of apparatus built in accordance with theteachings of the present invention, applicants constructed and operateda device substantially as shown in FIG. 1 of the drawing. In this tubestructure, the filament and cathode were operated at a potential of -16kilovolts with respect to the transparent electrically conductivecoating on the face of window member 11a. This transparent conductivecoating was connected to ground, as was the shell of the tube, toproduce a potential difference of 16 kv. between the cathode and theconductive coating on window member 112. Modulating input signals weresupplied between the cathode and grid of the tube, in accordance withthe teachings of the present application, to modulate the intensity ofthe electron beam emitted, and the resultant intensity modulated beamwas swept across a Teslar target member of 8 inch diameter and /i milthickness by a deflection voltage synchronized with the incoming videosignals.

Upon completion of the writing of the electrostatic charge distributionpattern on the target surface, the writing beam was shut off and thetube rotated to cascade the charged particles across the reverse side ofthe target surface. The charged particles adhered to the reverse side ofthe target surface in those areas thereof having opposite chargesthereon to produce a visible image of the electrostatic chargedistribution pattern. In this connection, the use of White opaqueTesla-r material is very desirable since it provides a high contrastwith the dark particles adhering thereto, thus increasing the visibilityof the resultant display. The resultant visible display persisted insubstantially the same form as originally prepared for a period of 168hours, thus clearly indicating the ability of the "target material toretain the discrete electrical charges thereon and hence to retain animage for an extended period of time.

To erase the display, the flood gun filament was operated at a potentialof 1.4 11V. relative to the tube face plate 11c, and a potential of +50volts was supplied to the front half of clamp ring 517 to cause thisring to serve as a collector electrode for the secondary emissionelectrons, as discussed above. Complete erasure of the display wasaccomplished in 0.1 second and the adhering particles on the reverseside of the target surface were removed therefrom on dissipation of theelectrostatic charged pattern.

The above information relative to the actual operation of the presentinvention clearly indicates the stability of the resultant imagedisplay. The present invention will have numerous applications where itis desired to produce a visible display of information Which istransmitted in the form of electrical signals. By virtue of the factthat only a single scan of the electrostatic target surface by themodulated electron beam is required to produce an electrostatic chargedistribution pattern suitable for producing a visible display inaccordance with the teachings of the present invention, and further inview of the persistence and stability of the resultant display, thepresent invention will be useful in numerous data processingapplications. For example, the present invention may be utilized toproduce a visible display at one or more Iv mote stations to whichelectrical signals, representing requested information, are sent from acentral file in the form of video signals in response to an inquiry fromsuch stations. Since only a single scan is required, a minimum amount ofcentral storage file time is involvedin transmitting the information tothe remote viewing locations, thus freeing both the'central file and thecommunication lines for transmission of information to other locations.Similarly, the stability of the display eliminates the need for repeatedscanning of the target surface by the modulated electron beam, andpermits the resultant display to remain for an extended period of timefor study, photography, projection or other use.

What is claimed is:

1. Apparatus for forming a visible image from an electricalinformation-bearing signal comprising an evacuated envelope, a source ofelectrons in said envelope, a target member of electrical insulatingmaterial disposed at one end of said envelope, a plurality ofelectrically charged particles of small size disposed in a chamber onthe opposite side of said target member from said electron source, meansfor directing said electrons in a beam toward said target member and forsweeping said beam across said tar-get member, means for modulating theintensity of said directed beam as a function of said electrical signalas said beam sweeps across said target to produce an electrostaticcharge distribution pattern on said target surface corresponding to saidinformation, means for maintaining said charged particles in saidchamber away from the influence of the electrostatic charge on saidtarget during sweeping of said beam across said target, and means forcascading said charged particles from said chamber over said targetmember upon completion of said charging of said target to cause saidparticles to adhere to said charged areas of said target to produce avisible image of said charged areas. V

2. Apparatus for forming a visible image from an electricalmformation-bearing signal comprisin g an evacuated envelope, saidenvelope having a transparent window at one end thereof, a source ofelectrons in said envelope, a target member of electrical insulatingmaterial disposed at said one end of said envelope and spaced from saidtransparent window to form a chamber, a plurality of electricallycharged particles of small size disposed in said chamber between saidtarget member and said window, means for directing said electrons in abeam toward said target member and for sweeping saidbeam across saidtarget member, means for modulating the intensity of said directed beamas a function of said electrical signal as said beam sweeps across saidtarget to produce an electrostatic charge distribution pattern on saidtarget surface corresponding to said information, means for maintainingsaid charged particles in said chamber away from the influence of theelectrostatic charge on said target during sweeping of said beam acrosssaid target, means for cascading said charged particles in said chamberover said target member upon completion of said charging of said targetto cause said particles to adhere to said charged areas of said targetto produce a visible image of said charged areas, and means for removingsaid electrostatic charge distribution pattern from said target surfaceto remove said visible image.

3. Apparatus for forming a visible image from an electricalinformationbearing signal comprising an evacuated envelope, saidenvelope having a transparent window at one end thereof, a source ofelectrons in said envelope, a target member of electrical insulatingmaterial disposed at said one end of said envelope and spaced from saidtransparent window to form a chamber, a plurality of electricallycharged particles of small size disposed in the bottom of said chamberbetween said target member and said window, means for directing saidelectrons in a beam toward said target member and for sweeping said beamacross said target member, means for modulating the intensity of saiddirected beam as a function of said electrical signal as said beamsweeps across said target to produce an electrostatic chargedistribution pattern on said target surface corresponding to saidinformation, means for maintaining said charged particles in saidchamber away from the influence of the electrostatic charge on saidtarget during sweeping of said beam across said target, means forrotating said envelope upon completion of said charging of said targetfor cascading said charged particles in the bottom of said chamber oversaid target member to cause said particles to adhere to said chargedareas of said target to produce a visible image of said charged areas,and means for removing said electrostatic charge distribution patternfrom said target surface to remove said visible image.

4. Apparatus for dorming a visible image from an electricalinformation-bearing signal comprising an evacuated envelope, saidenvelope having a transparent window at one end thereof, a source ofelectrons in said envelope, a target member of electrical insulatingmate-rial disposed at said one end of said envelope and spaced from saidtransparent window to form a chamber, a plurality of electricallycharged particles of small size disposed in said chamber between saidtarget member and said window, means for directing said electrons in abeam toward said target member and for sweeping said beam across saidtarget member, means for modulating the intensity of said directed beamas a function of said electrical signal as said bearn sweeps across saidtarget to produce an electrostatic charge distribution pattern on saidtarget surface corresponding to said information, means for maintainingsaid charged particles in said chamber away from the influence of theelectrostatic charge on said target during sweeping of said beam acrosssaid target, and drive means connected to said envelope for moving saidenvelope upon completion of said charging of said target for cascadingsaid charged particles from the bottom of said chamber over said targetmember to cause said particles to adhere to said charged areas of saidtarget to produce a visible image of said charged areas.

5. Apparatus for forming a visible image from an electricalinformation-bearing signal comprising an evacuated envelope, saidenvelope having a transparent window at one end thereof, a source ofelectrons in said envelope, a target member of electrical insulatingmaterial disposed at said one end of said envelope and spaced from saidtransparent window to form a chamber, a plurality of electricallycharged particles of small size disposed in the bottom of said chamberbetween said target member and said window, means for directing saidelectrons in a beam toward. said target member and for sweeping saidbeam across said target member, means for modulating the intensity ofsaid directed beam as a function of said electrical signal as said beamsweeps across said target to 10 produce an electrostatic chargedistribution pattern on for removing said electrostatic chargedistribution patsaid target surface corresponding to said information,tern from said target surface to remove said visible image.

means foa maintaining said changed particles in said chan1- her awayrfirom the influence of the electrostatic charge References (med m thefile of thls patent on said target [during sweeping of said beam acrosssaid 5 UNITED STATES PATENTS target, means for moving said target and aih g 1,818,760 Selenyi Aug. 11, 1931 particles u on completion of saidcharging f id target 2,618,551 Walkup Nov. 18, 1952 for cascading saidcharged particles fro t bottom 2,706,246 Klelnpercr Apr. 12, 1955 saidchamber over said target member to a e i P 2,716,048 Young Aug. 23, 1955ticles to adhere to said charged areas f i target 10 10 2,923,590 LorenzFeb. 2, 1960 produce a visible image of said charged areas, and means 957 1 Taubenslag et 1 Sept, 20; 19 0

1. APPARATUS FOR FORMING A VISIBLE IMAGE FROM AN ELECTRICALINFORMATION-BEARING SIGNAL COMPRISING AN EVACUATED ENVELOPE, A SOURCE OFELECTRONS IN SAID ENVELOPE, A TARGET MEMBER OF ELECTRICAL INSULATINGMATERIAL DISPOSED AT ONE END OF SAID ENVELOPE, A PLURALITY OFELECTRICALLY CHARGED PARTICLES OF SMALL SIZE DISPOSED IN A CHAMBER ONTHE OPPOSITE SIDE OF SAID MEMBER FROM SAID ELECTRON SOURCE, MEANS FORDIRECTING SAID ELECTRONS IN A BEAM TOWARD SAID TARGET MEMBER AND FORSWEEPING SAID BEAM ACROSS SAID TARGET MEMBER, MEANS FOR MODULATING THEINTENSITY OF SAID DIRECTED BEAM AS A FUNCTION OF SAID ELECTRICAL SIGNALAS SAID BEAM SWEEPS ACROSS SAID TARGET TO PRODUCE AN ELECTROSTATICCHARGE DISTRIBUTION PATTERN ON SAID TARGET SURFACE CORRESPONDING TO SAIDINFORMATION, MEANS FOR MAINTAINING SAID CHARGED PARTICLES IN SAIDCHAMBER AWAY FROM THE INFLUENCE OF THE ELECTROSTATIC CHARGE ON SAIDTARGET DURING SWEEPING OF SAID BEAM ACROSS SAID TARGET, AND MEANS FORCASCADING SAID CHARGED PARTICLES FROM SAID CHAMBER OVER SAID TARGETMEMBER UPON COMPLETION OF SAID CHARGING OF SAID TARGET TO CAUSE SAIDPARTICLES TO ADHERE TO SAID CHARGED AREAS OF SAID TARGET TO PRODUCE AVISIBLE IMAGE OF SAID CHARGED AREAS.